The phylogeny of echinoderm classes based on mitochondrial gene arrangements

Summary Previous analyses have demonstrated that, among the echinoderms, the sea star (class: Asteroidea) mitochondrial genome contains a large inversion in comparison to the mitochondrial DNA of sea urchins (class: Echinoidea). Polymerase chain reaction amplification, DNA cloning, and sequencing have been used to examine the relationships of the brittle stars (class: Ophiuroidea) and sea cucumbers (class: Holothuroidea) to the sea stars and sea urchins. The DNA sequence of the regions spanning potential inversion junctions in both brittle stars and sea cucumbers has been determined. This study has also revealed a highly modified tRNA cluster in the ophiuroid mitochondrial genome. Our data indicate mitochondrial gene arrangement patterns that group the sea cucumbers with sea urchins and sea stars with brittle stars. This use of molecular characters clarifies the relationships among these classes.     

Species composition and distribution of echinoderms (Echinodermata) in the upper subtidal zone of Kola Bay,Barents Sea

The species composition and patterns of distribution of echinoderms from the upper sublittoral zone to depth of 30 m in the southern and middle of Kola Bay in the Barents Sea were studied. In total, five species of starfishes, four species of brittle stars, three species of sea urchins and one species of holothurians were recorded. From the beginning of 20th century, under the impact of climate change and anthropogenic effect, the number of echinoderm species in the surveyed area decreased by two times, and the fauna has a more boreal character against the background of the domination of boreal-arctic species. The occurrence, population density and biomass of echinoderms, especially of common species, were several times less in the middle bend of the bay than in the southern one. The causes of this phenomenon have been discussed. The quantitative data (frequency of occurrence, number and biomass) for most of the species of echinoderms living in Kola Bay are given for the first time.     

Patterns of benthic mega-invertebrate habitat associations in the Pacific Northwest continental shelf waters: a reassessment

As human impacts and demands for ocean space increase (fisheries, aquaculture, marine reserves, renewable energy), identification of marine habitats hosting sensitive biological assemblages has become a priority. Epifaunal invertebrates, especially the structure-forming species, are an increasing conservation concern as many traditional (bottom-contact fishing) and novel (marine renewable energy) ocean uses have the potential to displace or otherwise impact these slow-growing organisms. The differences in mega-invertebrate species assemblages between high-relief rocks and low-relief sediments are well documented and likely hold for most marine environments. In anticipation of potential development of marine renewable energy faculties off Oregon and Washington (USA), a survey of the benthic invertebrate assemblages and habitats was conducted on three rocky reefs on the continental shelf of the Pacific Northwest, using video footage collected by remotely operated vehicle, to more finely characterize these assemblage–habitat associations. Benthic assemblages appeared to first group by depth (50–80 vs. 100–120 m), then by relief (consolidated rocks vs. unconsolidated rocks and soft sediments). Consolidated rocks were characterized at each site by a combination of various sponges, gorgonians, sea anemones and echinoderms; unconsolidated rocks were characterized at Grays Bank by sea anemones and burrowing brittle stars, and at Bandon-Arago by sponges and echinoderms; soft sediments were characterized at Grays Bank and Siltcoos Reef by sea whips and burrowing brittle stars, as well as pink shrimps and sea stars at Siltcoos Reef, and at Bandon-Arago by sponges, gorgonians and echinoderms. The results of this study will help classify and map the seafloor in a way that represents benthic habitats reflective of biological species assemblage distributions, rather than solely geological features, and support conservation and management planning.     

Lineage-Specific Evolution of Echinoderm Mitochondrial ATP Synthase Subunit 8

Peculiar evolutionary properties of the subunit 8 of mitochondrial ATP synthase (ATPase8) are revealed by comparative analyses carried out between both closely and distantly related species of echinoderms. The analysis of nucleotide substitution in the three echinoids demonstrated a relaxation of amino acid functional constraints. The deduced protein sequences display a well conserved domain at the N-terminus, while the central part is very variable. At the C-terminus, the broad distribution of positively charged amino acids, which is typical of other organisms, is not conserved in the two different echinoderm classes of the sea urchins and of the sea stars. Instead, a motif of three amino acids, so far not described elsewhere, is conserved in sea urchins and is found to be very similar to the motif present in the sea stars. Our results indicate that the N-terminal region seems to follow the same evolutionary pattern in different organisms, while the maintenance of the C-terminal part in a phylum-specific manner may reflect the co-evolution of mitochondrial and nuclear genes.     

Evolutionary modification of T-brain (tbr) expression patterns in sand dollar

The sand dollars are a group of irregular echinoids that diverged from other regular sea urchins approximately 200 million years ago. We isolated two orthologs of T-brain (tbr), Smtbr and Pjtbr, from the indirect developing sand dollar Scaphechinus mirabilis and the direct developing sand dollar Peronella japonica, respectively. The expression patterns of Smtbr and Pjtbr during early development were examined by whole mount in situ hybridization. The expression of Smtbr was first detected in micromere descendants in early blastula stage, similar to tbr expression in regular sea urchins. However, unlike in regular sea urchin, Smtbr expression in middle blastula stage was detected in micromere-descendent cells and a subset of macromere-descendant cells. At gastrula stage, expression of Smtbr was detected in part of the archenteron as well as primary mesenchyme cells. A similar pattern of tbr expression was observed in early Peronella embryos. A comparison of tbr expression patterns between sand dollars and other echinoderm species suggested that broader expression in the endomesoderm is an ancestral character of echinoderms. In addition to the endomesoderm, Pjtbr expression was detected in the apical organ, the animal-most part of the ectoderm.     

Effects of embryo energy,egg size,and larval food supply on the development of asteroid echinoderms

Organisms have limited resources available to invest in reproduction, causing a trade‐off between the number and size of offspring. One consequence of this trade‐off is the evolution of disparate egg sizes and, by extension, developmental modes. In particular, echinoid echinoderms (sea urchins and sand dollars) have been widely used to experimentally manipulate how changes in egg size affect development. Here, we test the generality of the echinoid results by (a) using laser ablations of blastomeres to experimentally reduce embryo energy in the asteroid echinoderms (sea stars), Pisaster ochraceus and Asterias forbesi and (b) comparing naturally produced, variably sized eggs (1.7‐fold volume difference between large and small eggs) in A. forbesi. In P. ochraceus and A. forbesi, there were no significant differences between juveniles from both experimentally reduced embryos and naturally produced eggs of variable size. However, in both embryo reduction and egg size variation experiments, simultaneous reductions in larval food had a significant and large effect on larval and juvenile development. These results indicate that (a) food levels are more important than embryo energy or egg size in determining larval and juvenile quality in sea stars and (b) the relative importance of embryo energy or egg size to fundamental life history parameters (time to and size at metamorphosis) does not appear to be consistent within echinoderms.     

Invasive tunicate restructures invertebrate community on fishing grounds and a large protected area on Georges Bank

Marine invasive species can profoundly alter ecosystem processes by displacing native species and changing community structures. The invasive tunicate Didemnum vexillum was first found on the northern edge of Georges Bank in 1998. It can form encrusting colonies on gravel substrates that are also a preferred habitat for a number of other invertebrates. In this study we used data collected via HabCam, a vessel-towed underwater imaging system, to investigate the distribution of D. vexillum and its relationship to other epibenthic macroinvertebrates in a portion of Georges Bank that includes fishing grounds and an area protected from bottom-fishing. This novel technology provides imaging of epibenthic species distributions in areas of the benthic environment that were previously unobservable. We found that D. vexillum density is negatively correlated with the Atlantic sea scallop (Placopecten magellanicus), barnacles (genus Balanus), the tube anemone (genus Cerianthus), the green sea urchin (Strongylocentrotus droebachiensis), the globular sponge of the genus Polymastia, and Bryozoa. However D. vexillum is positively correlated with Cancer spp. Crabs, the tube forming polychaete, Filograna implexa, and Asterias spp. sea stars. The hypothesis that D. vexillum restructures the invertebrate community is supported by principal components analysis, revealing it as a primary driver of variation in the community when present. Additionally, there is an effect of the closed area as compared to fishing grounds on the structure of the invertebrate community and the abundance of certain species as consistent with previous studies, bottom-fishing affects invertebrate community structure. Principal components analysis revealed that bottom-fishing also appears to weaken clustering among species in the invertebrate community as compared to the community structure in the closed area. Biodiversity in high gravel sites of the epibenthic environment, as measured by the Shannon diversity index, also declined with increasing D. vexillum percent cover, while the open and closed areas were not significantly different in their level of biodiversity. D. vexillum appears to be the key driver of biodiversity decline in the epibenthos when present, rather than other processes such as direct disturbance and extraction from dredging. This research evaluates ecological responses to the presence of an invasive tunicate and suggests that this invasive species is a major force in shaping the ecological interactions in invaded areas.     

Two more Posterior Hox genes and Hox cluster dispersal in echinoderms

Background

Hox genes are key elements in patterning animal development. They are renowned for their, often, clustered organisation in the genome, with supposed mechanistic links between the organisation of the genes and their expression. The widespread distribution and comparable functions of Hox genes across the animals has led to them being a major study system for comparing the molecular bases for construction and divergence of animal morphologies. Echinoderms (including sea urchins, sea stars, sea cucumbers, feather stars and brittle stars) possess one of the most unusual body plans in the animal kingdom with pronounced pentameral symmetry in the adults. Consequently, much interest has focused on their development, evolution and the role of the Hox genes in these processes. In this context, the organisation of echinoderm Hox gene clusters is distinctive. Within the classificatory system of Duboule, echinoderms constitute one of the clearest examples of Disorganized (D) clusters (i.e. intact clusters but with a gene order or orientation rearranged relative to the ancestral state).

Results

Here we describe two Hox genes (Hox11/13d and e) that have been overlooked in most previous work and have not been considered in reconstructions of echinoderm Hox complements and cluster organisation. The two genes are related to Posterior Hox genes and are present in all classes of echinoderm. Importantly, they do not reside in the Hox cluster of any species for which genomic linkage data is available.

Conclusion

Incorporating the two neglected Posterior Hox genes into assessments of echinoderm Hox gene complements and organisation shows that these animals in fact have Split (S) Hox clusters rather than simply Disorganized (D) clusters within the Duboule classification scheme. This then has implications for how these genes are likely regulated, with them no longer covered by any potential long-range Hox cluster-wide, or multigenic sub-cluster, regulatory mechanisms.

     

Mannan-binding lectins in the coelomic fluid of various species of Far Eastern echinoderms

A mannan-binding lectin activity was revealed in the coelomic fluid of the following echinoderm species inhabiting the coastal areas of the Sea of Japan, the holothurian Eupentacta fraudatrio, sea urchins Echinocardium cordatum, Strongylocentrotus nudus and S. intermedius, brittle star Amphipholis kochii, sea stars Asterina pectinifera, Lethasterias fusca, Lysastrosoma anthosticta, and Distolasterias nipon. It was shown that, concurrently with the general pattern of lectin interaction with branched bacterial mannans, there were also distinctions caused by the fine carbohydrate specificity of lectins. The obtained data preconditioned the further study of physical and chemical properties and structural features of the echinoderm MBL and the revelation of their role in the formation of the adaptive immune response and in other biological processes.     

中国海棘皮动物的种类组成及区系特点

棘皮动物是大型底栖动物的重要类群和组成部分.本文从种类组成和区系分布类型两个方面分析了各海区棘皮动物的多样性特点,讨论了温度、海流和水团等海洋环境因素对棘皮动物分布的影响.目前中国海域棘皮动物己记录有591种,包括海百合纲44种,海星纲86种,海胆纲93种,海参纲147种,蛇尾纲221种.黄、渤海和东海、南海的种类组成...     

Distribution of echinoderms and their larvae in the southwestern Peter the Great Bay, Sea of Japan

Based on results of processing planktonic and benthic samples collected in 1996 and 1997, a spatial distribution of echinoderms in the bottom and of their larvae in the plankton were collated for the water area of the Southern region of the Far Eastern State Biosphere Marine Reserve. Some correlation between distributions of the adult and larval sea star Asterias amurensis in July was revealed. At the same time, there was no correlation between distributions of larvae and adult individuals of the brittle star Ophiura sarsi and sea urchin Echinocardium cordatum, which are most abundant in the area. The size structure of bottom populations of the brittle stars O. sarsi and Amphiodia fissa in the studied area was assessed. The correlation coefficient between the distribution of young-of-the-year and the population density was 0.47 in O. sarsi and 0.74 in A. fissa respectively, which implied a selective settling of larvae of those species in areas inhabited by adult brittle stars. Recruitment of bottom populations from 1996 spawning was 5% in O. sarsi and 3.3% in A. fissa.     

Habitat-based submersible assessment of macro-invertebrate and groundfish assemblages at Heceta Bank, Oregon, from 1988 to 1990

Exploitation of groundfish off the U.S. Pacific coast reached maximum levels during the 1990s, resulting in severe declines in at least nine species of groundfish. From 1988 to 1990, we used the 2-man submersible Delta to make 42 dives and run replicate visual belt transects at six stations ranging from 67-360 m in depth at Heceta Bank on the outer continental shelf of Oregon. We identified four major habitats and associated benthic macroinvertebrate and groundfish assemblages: (1) shallow rock ridges and large boulders (< 100 m deep) dominated by basket stars, juvenile rockfishes, yelloweye rockfish, and lingcod; (2) mid-depth small boulder-cobbles (100-150 m) dominated by crinoids, brittle stars, rosethorn, pygmy/Puget sound, and canary rockfishes; (3) deep cobble (150-200 m) dominated by crinoids, brittle stars and various small rockfish species, and (4) deep mud slope (> 200 m) dominated by fragile urchins, sea cucumbers, shortspine thornyhead, and flatfishes. Although substantial interannual variation in groundfish abundance among seafloor types was evident in the 12 most abundant and/or commercially important fish taxa sampled, high variance resulted in statistically significant differences among years only in juvenile rockfishes. These data provide a baseline for future comparisons exploring long-term change this continental-shelf ecosystem.     

Activity, feeding behaviour and diet of Ogcocephalus vespertilio in southern west Atlantic

The Brazilian batfish Ogcocephalus vespertilio is a nocturnal and early morning predator on bottom invertebrates, staying stationary and hidden in rock holes, crevices or among bottom rocks during the day. While active, it searches for prey walking along the bottom with the help of its specialized paired fins, with the illicium protracted and oscillating or exploring the substrate. The prey are either snapped up from the bottom, after visual detection, or dug out with use of the mouth and rostrum. It feeds on crustaceans (hermit crabs, true crabs, shrimps, amphipods, porcelain crabs, isopods and mysid shrimps), molluscs (snails, sea slugs and clams), polychaete worms (mostly Errantia) and echinoderms (sea urchins and brittle stars).     

Overgrazing of Kelp Beds Along the Coast of Norway

The aim of this study was to better understand the down-grazing of kelp beds by sea urchins (Strongylocentrotus droebachiensis) along the coast of Norway. Barren grounds were first observed in sheltered areas along the coast of the counties of Trø ndelag, Nordland and Troms in 1974. In the 1980s, the barren grounds spread to areas more heavily exposed to waves. In the 1990s, the kelp beds were re-established in some localities in southern Trø ndelag, initially in wave-exposed areas. In the northernmost parts of Norway, i.e. the counties of Troms and Finnmark, the barren ground areas may still be increasing. Crabs (Cancer pagurus) and common eiders are the most common predators on urchins. Predation on sea urchins in kelp beds is probably not among the factors that limit the sea urchin populations. Along the coast of Nordland and further north, sea urchins are infected by nematodes, resulting in a low, but significant increase in their mortality. No re-growth of kelp beds has been found in the most infected areas. In the late 1960s and the early 1970s, a high occurrence of echinoderm larvae was observed in deeper waters. This was a period with cold water, which may have caused high recruitment of sea urchins. The bet-hedging life strategy of sea urchins may account for the sudden increase in the size of the populations. In the present paper I propose the hypothesis that higher individual growth rates and higher mortality rates in the south than in the north may explain the decrease in the populations, which may in turn account for the re-growth of kelp in the southern areas.     

Southeastern Chukchi Sea (Alaska) epibenthos

Epibenthos of the southeastern Chukchi Sea, inclusive of Kotzebue Sound, was sampled in 1976. Crustaceans dominated abundance while echinoderms, mainly sea stars, dominated biomass. Spatial distribution of fauna was determined by cluster analysis. Scavenger-predators were dominant trophic groups, although suspension feeders dominated some regions. Unexpected high abundance and biomass under Alaska Coastal Water and factors related to presence and distribution of fauna are discussed. Dissimilarities between the benthic systems of the southeastern and northeastern Chukchi Seas are attributed to more complex water mass and flow patterns in the southern system. Entrained particulate organic carbon disperses through the area to support an abundant and apparently highly productive benthic fauna, which sustains resident and transient populations of demersal fishes and marine mammals. Epibenthos was sampled again in 1998 and, although little change was apparent in community composition, many taxa had higher abundance and biomass than 22 years earlier, a trend similar to findings observed in the northeastern Bering Sea.Electronic Supplementary Material Supplementary material is available for this article at     

Predation of the sea urchin Heliocidaris erythrogramma by rock lobsters (Jasus edwardsii) in no-take marine reserves

The formation of sea urchin ‘barrens’ on shallow temperate rocky reefs is well documented. However there has been much conjecture about the underlying mechanisms leading to sea urchin barrens, and relatively little experimentation to test these ideas critically. We conducted a series of manipulative experiments to determine whether predation mortality is an important mechanism structuring populations of the sea urchin Heliocidaris erythrogramma in Tasmania. Tethered juvenile and adult sea urchins experienced much higher rates of mortality inside no-take marine reserves where sea urchin predators were abundant compared to adjacent fished areas where predators were fewer. Mortality of tagged (but not tethered) sea urchins was also notably higher in marine reserves than in adjacent areas open to fishing. When a range of sizes of sea urchins was exposed to three sizes of rock lobsters in a caging experiment, juvenile sea urchins were eaten more frequently than larger sea urchins by all sizes of rock lobster, but only the largest rock lobsters (> 120 mm CL) were able to consume large adult sea urchins. Tagging (but not tethering) juvenile and adult sea urchins in two separate marine reserves indicated that adult sea urchins experience higher predation mortality than juveniles, probably because juveniles can shelter in cryptic microhabitat more effectively. In a field experiment in which exposure of sea urchins to rock lobster (Jasus edwardsii) and demersal reef fish predators was manipulated, rock lobsters were shown to be more important than fish as predators of adult sea urchins in a marine reserve. We conclude that predators, and particularly rock lobsters, exert significant predation mortality on H. erythrogramma in Tasmanian marine reserves, and that adult sea urchins are more vulnerable than smaller cryptic individuals. Fishing of rock lobsters is likely to reduce an important component of mortality in H. erythrogramma populations.     

Heterochronic activation of VEGF signaling and the evolution of the skeleton in echinoderm pluteus larvae

The evolution of the echinoderm larval skeleton was examined from the aspect of interactions between skeletogenic mesenchyme cells and surrounding epithelium. We focused on vascular endothelial growth factor (VEGF) signaling, which was reported to be essential for skeletogenesis in sea urchin larvae. Here, we examined the expression patterns of vegf and vegfr in starfish and brittle stars. During starfish embryogenesis, no expression of either vegfr or vegf was detected, which contrast with previous reports on the expression of starfish homologs of sea urchin skeletogenic genes, including Ets, Tbr, and Dri. In later stages, when adult skeletogenesis commenced, vegfr and vegf expression were upregulated in skeletogenic cells and in the adjacent epidermis, respectively. These expression patterns suggest that heterochronic activation of VEGF signaling is one of the key molecular evolutionary steps in the evolution of the larval skeleton. The absence of vegf or vegfr expression during early embryogenesis in starfish suggests that the evolution of the larval skeleton requires distinct evolutionary changes, both in mesoderm cells (activation of vegfr expression) and in epidermal cells (activation of vegf expression). In brittle stars, which have well‐organized skeletons like the sea urchin, vegfr and vegf were expressed in the skeletogenic mesenchyme and the overlying epidermis, respectively, in the same manner as in sea urchins. Therefore, the distinct activation of vegfr and vegf may have occurred in two lineages, sea urchins and brittle stars.     

THE DISTRIBUTION OF WHITE-SIDED (LAGENORHYNCHUS ACUTUS) AND COMMON DOLPHINS (DELPHINUS DELPHIS) VS. ENVIRONMENTAL FEATURES OF THE CONTINENTAL SHELF OF THE NORTHEASTERN UNITED STATES

Sightings of white-sided ( Lagenorhynchus acutus ) and common dolphins ( Delphinus delphis ) from survey vessels operating on the continental shelf of the northeastern United States were recorded during spring and fall of six years. Distributions of these sightings were compared with sea surface temperature and salinity, and bottom topography. The apparent geographic distributions of the two species are complementary, although there is a broad overlap. White-sided dolphins occurred primarily within the Gulf of Maine, but also on Georges Bank and in the mid-Atlantic region. Common dolphins were abundant within a broad band paralleling the continental slope (100–200 m depth contour) from latitude 35°N to the northeast peak of Georges Bank. Sightings of this species were distributed primarily along the edge of the continental shelf south of 40°N in spring and north of this latitude in fall. Few sightings of common dolphins occurred in the Gulf of Maine.
Although both species of dolphins were sighted more frequently in areas of high sea floor relief, white-sided dolphins occurred in areas where sea surface temperatures and salinities are low while common dolphins were sighted in warmer, more saline waters. However, these environmental conditions may be only secondarily influencing dolphin distribution. Seasonal variation in sea surface temperature and salinity, and local nutrient upwelling in areas of high sea floor relief may affect preferred prey abundances, which in turn may affect dolphin distribution.